Pigmented moisture curable coatings have been in use for at least the last 25 years. These coatings fall mainly into two distinct groups. Single component coatings are those which are shipped in a ready-to-use condition and which must be maintained in a substantially moisture free environment to prevent premature curing. Two component coatings are shipped in separate packages and require the user to mix the components just prior to use.
The main problem with the two component systems has always been the on-site mixing. Improper ratios of components when mixed often renders the coating inefficient or at times useless.
In an effort to overcome user error, one component systems were introduced, beginning with the coating described and claimed in U.S. Pat. No. 3,479,325, which disclosed the mixing of a monomeric isocyanate compound with a polymeric compound containing free --OH groups, then adding a polyisocyanate solution to remove residual water. The main problem with the one component systems was and still is the necessity of strict controls in the mixing of the reagents. Other problems involve the length of time needed to produce a batch of coating and limited shelf life.
U.S. Pat. No. 4,304,706 discloses a method for producing one-component coatings which involves a controlled three-step process. As disclosed in this patent, a measured amount of a monomeric diisocyanate and a polyol are mixed in a pigment dispersion so that excess unreacted --OH groups are present. The resulting dispersion is then mixed with enough of a polyisocyanate to consume these --OH groups and to leave an excess of free --CNO groups to react with moisture when the coating is to be used. This process speeds up production time, but still requires strict controls in a multiple step process to produce an efficient and usable coating.
Other patents which disclose polyurethane coatings and methods of manufacture are found in the accompanying prior art sheet.